A telecommunication scheme called “Wideband Code Division Multiple Access (W-CDMA)” is used to perform data communication between a wireless communication apparatus, such as a mobile phone, and a base station. In telecommunication using the W-CDMA, transport channels (TRCHs) are identified by spreading codes each allocated to a corresponding TRCH and data communication is performed using a plurality of TRCHs that share a single frequency band.
However, in an actual mobile communication environment where, for example, radio interference from another cell may occur, it is difficult to always maintain the quality of signals that the wireless communication apparatus receives from the base station at a desired level. To solve the problem, the wireless communication apparatus measures a signal-to-interference ratio (SIR) and performs inner loop control to set the SIR closer to a target SIR.
Because the moving speed and the communication environments are subjected to change, the SIR to produce the desired quality (block error rate: BLER) is not fixed. To cope with these changes, the wireless communication apparatus measures the BLER and performs outer loop control in which, if the measured BLER is worse than a target BLER, the wireless communication apparatus increases the target SIR and, if the measured BLER is better than the target BLER, the wireless communication apparatus decreases the target SIR (see, for example, Japanese Laid-open Patent Publication No. 2006-80924).
In the existing wireless communication apparatus, the criterion for the outer loop control differs among TRCHs; therefore, if a plurality of TRCHs are present, the wireless communication apparatus selects a reference TRCH from the plurality of TRCHs and performs the outer loop control in accordance with the criterion of the selected TRCH.
If a wireless communication apparatus is designed to select a specified TRCH from a plurality of TRCHs, the wireless communication apparatus selects the specified TRCH using, for example, a type of data (e.g., audio data and image data) to be transmitted using the TRCHs or a combination of the types. If, for example, a TRCH that transmits audio data and a TRCH that transmits image data are present, the wireless communication apparatus selects the TRCH that transmits image data.
A technology is currently used that measures BLERs of individual TRCHs, selects a TRCH having the worst BLER, and performs the outer loop control so that no TRCH has a BLER lower than the target BLER (see, for example, Japanese National Publication of International Patent Application No. 2007-500969).
However, because, in the above-described conventional technologies, the reference TRCH is selected in accordance with expected conditions, it is impossible to cope with an unexpected condition (e.g., an unexpected combination of types of data included in a packet). This may prevent implementation of the most-suitable outer loop control.
Moreover, although the method of measuring the BLERs of the individual TRCHs and selecting the most-suitable TRCH using the measured result as described above is effective, because a long time is needed to measure the BLERs, there is possibility that there is an increase in the time necessary to obtain a stable BLER from the start of communication.
There is an obvious need for a technology that selects the most-suitable TRCH for the outer loop control in accordance with a variety of conditions that are set related to the TRCHs.